This invention relates to ultrasonic transducer apparatus used in the measuring of bolt elongation. More particularly, this invention relates to apparatus for vacuum coupling an ultrasonic transducer to a bolt for measurement of elongation of the bolt.
The technology, including apparatus and methods, of ultrasonically measuring the elongation of bolts to determine load or tightening of the bolt is well known. Apparatus and methods of varying degrees of sophistication are shown, for example in U.S. Pat. Nos. 3,759,090, 3,810,385, 3,969,810, 4,423,518 and 4,471,651 (that list of prior art patents being intended merely as a sampling and not intended to be a comprehensive listing of prior art patents in the field).
Regardless of the level of sophistication of the technology, it all uses an ultrasonic transducer in contact with the bolt whose elongation is to be ultrasonically measured. In response to electronic input pulses, the transducer sends an ultrasonic pulse along the length of the bolt, senses the echo from the end of the bolt, and delivers a measurement signal to the measuring and detecting circuitry of the apparatus.
A recognized problem area in the technology of ultrasonic measurement of bolt elongation is in maintaining firm and continuous contact between the transducer and the bolt being measured. Reliable measurements can not be obtained if firm and continuous contact is not maintained between the transducer and the head of the bolt. The prior art has typically used a couplant material such as oil or glycerine between the bolt and a means for holding the transducer in place while the ultrasonic measurement is made. The holding means have been mechanically or magnetically accomplished by threaded connections or angular magnets around the transducer. While the use of such holding techniques is generally effective, it has a number of drawbacks such as mechanical mounting which is difficult to accomplish, failure of magnetic means on nonmagnetic materials and attractions of magnetic debris on the transducer face.